Benchmarking sunflower water productivity in semi-arid environments

GRASSINI, P.; HALL, A.J.; MERCAU, J.L.

FIELD CROPS RESEARCH

Elsevier Science B.V.

Lugar: Amsterdam; Año: 2009 vol. 110 p. 251 - 262

0378-4290

Appropriate benchmarking is essential for evaluating the efficiency with which crops use water and foridentifying constraints, other than water, to crop yield. No benchmark exists for sunflower. Boundary andsimulation analyses were used to quantify the water productivity of sunflower crops grown in theWestern Pampas (semiarid central Argentina). The approach involved the use of a large database(n = 169) collected in farmers’ fields over a period of 4 years, and the application of a crop simulationmodel in combination with actual weather and soil data. Using field data, an upper bound of 8 kggrain ha1 mm1 for water productivity, with an apparent seasonal soil evaporation of 75 mm, wasdefined. Seasonal water supply exceeded maximum expected seasonal crop requirements (ca. 630 mm)for many crops, and a majority of crops with <630 mm of available water during the season had waterproductivities considerably lower than the upper bound. The field data-based upper bound wasindistinguishable from that obtained using yields for a set of 47 simulations using observed initial valuesfor soil water and nitrogen profiles. Simulation confirmed the main features of the boundary-analysisapplied to field data, and many simulated crops had yields that fell below the boundary function, evenwhen simulated yield was plotted against simulated seasonal evapotranspiration or transpiration. Longterm(33-year) simulation analyses for two sites showed that most sunflower crops in the area aresubjected to episodes of transient and unavoidable water stress after floral initiation. High levels ofavailable soil water at sowing moderate, but in most years do not eliminate, these exposures to waterstress. Yield gaps with respect to the boundary function were associated with deficient or excessiverainfall during grain filling, and other, non-water related, factors such as inadequate crop nutrition, bioticstresses, low photothermal quotients during the interval close to anthesis, and lodging. A grain yield/seasonal evapotranspiration plot for a large (n = 154) data set from experiments conducted by others infive separate environments globally, suggests that the boundary function found for the Western Pampasis broadly applicable. Sunflower water productivity, corrected for oil-synthesis costs and seasonal vapourpressure deficit differences, approximates that of winter cereals grown in Mediterranean environments. 2008 Elsevier B.V. All rights reserved.